Exergy-Based Efficiency Validation for TES Systems: Exergetic COP and Destruction Mapping

Exergy—unlike energy—is the *usable* portion of heat or work constrained by ambient conditions (T₀, P₀). For TES, exergy comes from temperature lift above ambient (physical exergy) and phase change potential (chemical exergy in PCMs). A 400°C molten salt charge has ~1.8 MJ/kg of thermal exergy, while the same heat at 120°C holds only ~0.35 MJ/kg—even if total energy is identical.

Exergetic COP compares what you *get back usefully* (e.g., saturated steam at 300°C for distillation) to what you *put in usefully* (e.g., superheated salt at 565°C). Unlike energy-based COP, it penalizes low-grade recovery and temperature glide. Destruction mapping uses local entropy generation (Ṡ_gen = Ṡ_out − Ṡ_in − Ṡ_transfer) to quantify irreversibility in each subsystem—critical because PCM hysteresis or salt stratification can concentrate >90% of total destruction in <15% of volume.

Advanced validation requires coupling transient CFD (ANSYS Fluent or OpenFOAM) with exergy-aware boundary conditions and property databases compliant with IAPWS-95 (water/steam) or NIST Molten Salt Database. Real-time validation now leverages digital twins fed by fiber-optic distributed temperature sensing (DTS) with ±0.5 K accuracy—enabling destruction hotspot detection at <0.1 m resolution in 50 m tall tanks. ISO/IEC 17025-accredited labs now report exergy uncertainty budgets per ASME PTC 30-2, treating ambient condition drift (ΔT₀ > 2 K) as a dominant Type B uncertainty contributor.